Apparatus for recording seismic waves



oct. 17, 1944. i J, P. MINTON 2,360,507

APPARATUS FOR RECORDING SEISMIC WAVES Oct. 17,'1944. J. P. MIN-roN 2,360,507

v I APPARATUS FOR RECORDING SEISMIG WAVES Filed Oct. l, 1941 3 Sheets-Sheet 2 ITV Oct. 17, 1944. J. P. MINToN 2,350,507

APPARATUS FOR RECORDING SEISMIC WAVES Filed Oct. 1 1941 3 Sheets-Sheet 3 i rf/icf v v Ann/nm 1 AL v Patented ct. 17,1944A RECORDING SEISMIC APPARATUS FOR WAVES .lohn P. Minton, Dallas, Tex.. assignor to Socony- Vacuum Oil Company, Incorporated, New York, N. Y., a corporation of New York Application October 1, 1941, Serial No. 413,116

Claims.

This invention relates generally to geophysical prospecting and more particularly to a system and apparatus for recording seismic waves.

In the art of reflection seismic surveying, in-

terpretation of records is often based on thel faulting. Where such conditions exist, it has been foundthat by mixing the geophone outputs from a selected number of stations, it is possible to trace a reection entirely across the record Afrom the first to the last trace.

Additionally, in some areas considerable lensing of substrata is encountered. Where such conditions exist errors are frequently made as a result of the interpreter confusing reflections `from the stratum being profiled with lenses which lie adjacent the stratum. By properly mixing the signals from the individual detecting stations, such possibility of error is eliminated.

Heretofore, in order to elect a mixing ofsignals it has been necessary to connect groups of two or three detecting stations in multiple, and record the combined output of the geophones on a single trace.' This, however, Was objectionable since each trace recorded on the seismogram would represent independent groups o f detecting stations corresponding to the number selected in such a manner that there Would be no overlapping between traces. Additionally, obtainable data was reduced by a factor equal to the number of stations connected in series.

By means lof the instant invention it is possible to overcome these diiculties and-produce a record that will have one trace less than the number of detecting stations and which will represent any selected grouping that will overlap Lfrom the first to the last trace.

ITL-352) recording the rectied output signals after the carrier frequency has been eliminated.

Still another object of this invention resides in the provision of detecting means in each of the amplifier circuits which consist of full wave copper oxide rectiers.

Another object of this invention resides in the novel manner of -mixing adjacent amplifier channels through the medium of the copper oxide rectiers without producing cross-feeding to channels outside of the selected group.

Still another object of this invention resides in the provision of a means of recording seismic Waves from a plurality ofdetecting stations by combining the signals from a succession of `a selected number of stations in sucha manner that each succeeding trace recorded will be an overlap of the stations recorded on the first trace but for one station.

Still another object of this invention resides in the provision of .a system of recording seismic waves which is sufficiently flexible that any desired method of mixing can be accomplished without producing undesirable cross-feeding to traces outside of the selected group.

Other objects and advantages will become apparent from the following detailed description when considered with the accompanying drawings in which:

Figure 1 'shows a circuit diagram for -the rst and an intermediate channel of an electric seismograph recording system in which mixing is effected by triples;

Figure 2 -is a Wiring diagram of a' plurality of adjacent channels in which mixing is elected by triples in such a manner that overlapping is obtained from the first to the last channel; and

Figure 3 is a wiring diagram illustrating the manner in which mixing is effected by doubles which overlap. y

Referring to Figure 1 of the drawings, there are shown two channels of an electric seismo- Therefore, the primary object of this invention ing seismic waves that are detected by modulating a high frequency carrier wave, amplifying the high frequency earrier'wave, then rectiying andA graph. These channels are the type which utilize inductance type geophones G1 andGn which modulate a carrier wave which'is supplied by the oscillator j and which isof relatively high frequency compared to the seismic Waves. The frequency of the carrier wave may be in the order of 500 to 1000 cycles. Modulation ofthe carrier wave is effected by a change in the inductance'of the coils Il) and Il, and l2 and I3, by relative movement between the cores I4 and I5, and IE and l1, of the coils and the armature, effected by oscillations produced by the seismic waves. Coils Il) and Il of the geophoney G1 form two arms of a. reactance bridge circuit, the other two arms being formed by the sections I8 and I9 of a resistance R1. This reactance bridge circuit may be used in balanced or unbalanced condition by adjusting the contactor on the resistance R1. The output signals from the geophone vwG1 which is a high frequency carrier wave modulated-at the frequency of the seismic waves is, by means of the conductors 21,'

conducted to a. band pass lter 22. The lter 22 passes both the carrier and side band frequencies in either the balanced or unbalanced operation of the geophones Gi-Gn. This iilter eliminates any extraneous frequencies thattrnay be present outside the pass band.. From the band pass filter 22, the signals pass into the amplier 23 Where they are amplified. After ampliiication, the signals are detected by means of a full Iwave copper oxide rectier 24. The outputsignals from the copper oxide rectifier are conducted by means of conductors 25 to the iilter 26, wherethe carrier wave, when present, fand other unwanted frequencies are eliminated and, if necessary, further amplified in the amplifier 21 and 'recorded by the recorder 28 on a moving sensitized paper or photographic film in .coordinationI with time.

Each of the geophones Cri-Gn may be of the type disclosed and claimed in my copending application Serial Number 517,731, iiled January |0, 1944, for Geophysicall prospecting 'apparatus, this said application being a continuation-in-part of an earlier filed application, Serial Number 411,766'. l

Geophone G1 in Fig. 1 represents the flrst'geophone in a spread made up of a plurality of geophones collaterally spaced from a source of creation of seismic waves. Geophone Gnfis another geophone in the same spread which for purpose ofy illustration may be any number of stations further.. removed from the point of creation of the seismic waves thang-the geophone G1. In like manner, Gn modulates the high frequency carrier wave that is supplied by the source f in a reactance bridge circuit which comprises the coils l2 and I3 of the geophone and sections 29 and 3ll.xof the resistance Rn. Balancing o f the reactance bridge circuit is effected by adjustment of the contactor 3|. The output signals fromthe reactance bridge circuit are passed through the band pass filter 32, which acts simithat is adapted to amplify and detect signals from a geophone Gn-z, not shown. These connections' are' described in detail in the following paragraphs. t

This connection is effected in the manner illustrated in Figure 2. The rectiiier is con--vv With an 'arrangement of connections described labove and illustratedin Figure 2, it is possible to record on trace 11.-.2 a record thatis a composite of the output signals' from geophones G11-2, Gfx-1, and Gn. The trace ln-l will be a composite of the signals from geophones G11-1, Gn and Gn+1, and the trace n will be a composite of signals from geophones Gn, Gn+1 and Gnu. Since these copper oxide rectifiers are unidirec- .tional conductors, the output signals cannot feed back through them into their inputs from which -theywould affect other traces.

Therefore, it becomes readily apparent that adjacent traces will have recorded on them signals from tn'ples which overlap but for one station in each instance. The mixing can be carried throughout the spread to produce a seismogram that will emphasize the reiiections recorded on the traces fromthe first to the last trace, thereby enabling the interpreter to easily follow a group of eections from those detected at the beginning of the spread to those detected at the last geophone in the spread Without the possibility of erroneously selecting impulses on the last trace that do not correspond to the reiiections recorded on the first trace.

Rectifers 40, 4I and 42 represent still another triple, the composite signals from which are recorded on trace n+1, while rectiflers 43 and 44 are a part of another triple, the composite output signals from which are recorded on trace n+2, and rectifier 45 is a partv of still another triple, the composite output signals from' which are recorded on the trace 1|.-|3.

The instant invention thus far has been described in connection with the use of triples. As shown in Figure 3, mixing by doubles may be effected. The output from two adjacent seismograph channels are combined by means of the rectifiers 46 and 41 and the conductors 48, and Vconducted to a iilter 49 by means of conductors 50. The output from the iilter- 49 is then amplified by the amplifier 5| and recorded on trace No. 1 of a seismogram by means of a recording galvanometer, not shown. Rectiiiers 41 and 52 are connected in parallel on the second channel. Likewise, the inputs of rectiers 54 and 58 are connectedtogether on channel No. 3. The outputs of rectiers 52 and 54 are connected together, filtered in 56-to exclude the carrier, amplied by 51 and recorded as trace No. 2, of the seismogram. In any individual horizontal array of the rectifiers, the inputs are all connected in parallel to the corresponding vchannel number. In the individual vertical arrays, the outputs are connected together leading to the appropriately indicated trace. Filters 49 and 56, as well as the corresponding filters 1U in the other channels are for the purpose of excluding the carrier frequency, .when present, and other unwanted frequencies, in order that the signals may be amplified and recorded corresponding to the seismic waves. Rectiiiers 54 and 58 are connected kin parallel in channel No.-

l"-3.gf an electric seismograph. The output from nected by means of conductors 38 to a second rectifier 58 vis, by means of conductors 59, connected to rectier 60 in channel No. 4. 'The composite output of these two rectiflers are in the manner described above recorded on trace No. 3. In like manner, ythe output from the doubles comprising rectiers l6I and 52, vand S14-and 64, are respectivelyl recorded on traces Nos. 4 and 5 ofthe seisrnogram, while the output from rectier will be unmixed Asignals and will be recorded on trace No. `(-of the seismogram. Any.

number of successive stations in the spread can in this manner be mixed by doubles so that an overlapping is effected from the rst to the last station.

Although the present invention has been described in connection with mixing by doubles and triples, it is obvious from the above detailed description when taken with the drawings to those skilled in the art, that mixing by quadruples or any other desired combinationcan be effected.

I claim:

1. In an apparatus for recording. seismic waves that have been created in theearths surface anddetected at a plurality of stations by modulating a common high frequency carrier wave at the frequency of the seismic waves, amplifiers for independently adllplfying the resultant signals from each station, at least one balanced bridge full wave rectifier in eachampler circuit, means for mixing the output of one rectifier in each of a succession of adjacent channels in groups comprisinga selected number of amplifiers, means for filtering the carrier Wave from the mixed composite signal, and means for recording the outputI signals from each ilter on independent traces of a seismogram.

2. In a system, for recording seismic lWaves which have been created in the earths surface and detected at a, plurality of stations by modulating a common high frequency carrier Wave at the frequency of the seismic Waves, having amplifiers for independently amplifying the resultant signals from each station and recording devices for producing lindependent tracesof a seismogram, the combination of means for producing an output signal for recordation on a trace of said seismogram which is -a composite signal from a group of said stations comprising a balanced bridge full wave rectifier in each amplifier circuit in said group, an output circuit, means connecting said full Wave rectiers in parallel with each other and with said output circuit, means for filtering the carrier wave from the mixed composite signal applied to said output circuit, and means for applying said composite signal to one of said recording devices for recordation on a trace of said seismogram.

3, In a system for recording seismic Waves Which have been created in the earths surface and detected at a plurality of stations by modulating a common high frequency carrier wave other and with said output circuit, means for filtering the carrier wave fromv the mixed composite signal applied tovsaid oatput circuit, and

means for applying said composite signal to oneof said recording devices for recordation on a trace of said seismogram.`

4. In a system, for recording seismic Waves which have been created in the earths surface and detected at a plurality of stations by modulating a. common high frequency carrier wave at the frequency of the seismic Waves, having amplilers for independently amplifying the resultant signals from each station and means for recording output signals on independent traces of a seismogram, the combination of means for electrically producing a mixed composite signal from selected groups of said amplifiers comprising a balanced bridge full Wave rectifier lfor the output signals of each amplifier of each group, and an additional balanced bridge fulll Wave rectier for the outputsignals of each. am-

at the frequency of the seismic Waves, which system includes amplifiers for independently amplifying the resultant signals from each station-and recording devices for producing inde- 1 pendent traces of a seismogram, the combination of means for producing an output signal for recordation on a trace of said seismogram which is a composite signal from a group of said stations comprising a balanced bridge full- Wave copper oxide r'ectier in each amplifier circuit in said group, an output circuit, means connect- -ing said full Wave rectiers in parallel Iwith each plifier circuitwhiclf also 'forms a part of another `group for production. of another mixed composite signal', an outputhcircuit for each group of amplifiers for operating said recording means to produce a single trace of said seismogram,means connecting in parallel with each said output circuit one of said full WaveV rectiflers'in each amplifier circuit included in one of said groups, and means for filtering the carrier'wave from the Amixed composite signal from each said group whereby there are recorded on independent traces of said seismogram said mixed composite signals 'from each group of said amplifiers.

5. Ina system for recording seismic waves which have been created in the earths surface and detected at a plurality of 'stations by modulating a common high frequency carrier wave at the frequency of the seismic waves, which system includes amplifiers for independently amplifying the resultant signals from each station and means for recording output signals on independent traces of a. seismogram, the combination of means for electrically producing a mixed composite signal from each of a plurality of selected groups of -said amplifiers comprising a balanced bridge full Wavecopper oxide rectifier for the amplified output signals of each amplifier of each group, and an additional balanced bridge full Wave -copper oxide rectifier for the output signals of each amplifier which also formsl a part of .another group for production of another mixed composite signal, an output circuit for each group of ampliers for operating said recording means to produce a single trace of said seismogram, means connecting in parallel with each said output circuit one of said full wave rectiiiers in each amplifier circuit included in one of said groups, and means for filtering the carrier wave from the mixed composite signal fromy each said group, whereby there is recorded on each independent trace of the seismogram said mixed composite signal from each 

